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Old 12-17-2007, 12:19 AM   #1
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Default Interesting IAC learnings

I've had a cold start problem on the Zilla for quite some time. Probably over 6 months. A month or so ago, I swapped a different IAC in (I have 3 spares) and it made no difference.

I chalked it up to the ported heads, rockers, etc, and the fact that the ICM rattles the injectors for the first 400 rpm'* before the PCM can take over. Maybe the ICM (which can't learn) doesn't know what to do with my bastardized setup.

I know I was running lean on startup. Wideband O2 tells me that every day, and after the 6th or 7th start attempt, it settles in to the proper AFR. So what if I block off part of the IAC passage? That'* a though that occurred to me.

I had a good 'winter opportunity' today, as I'd organized my garage for the engine swap, and only had to move my engine stand and engine hoist out of the way to install the new DVD deck in the SLE. Later (just a bit ago) I took that opportunity to pull the Zilla in and look into the feasibility of blocking off part of the IAC passage to help start the lean start issues.

I decided instead to compare IAC'*. Call it pin ABCD from left to right as installed in the TB, looking at the front of the car.

A-B was 48 ohms on all three spares. C-D was the same. On ALL THREE spares.

On the Zilla, A-B was 52 ohms, and C-D was 53. So I hooked up one of my spares to the harness, and cycled the ignition. Damn thing ejected the plunger and spring. They launched all the way to my alternator. Tried another, and it did the same thing. Must be normal sez me.

So I screwed one back in, and carefully aligned the grooves and notches, then installed it in a spare TB, put the screws in, and cycled the ignition a few times. It went back together ok, but was extended farther than the one that just came out. Ok, sez me, that'* what I want. Less air.

I installed it in the Zilla, and it wouldn't start. Fully closed. So I cracked the throttle with my foot a bit, started right up, then feathered the throttle down until the IAC took over and maintained my AFR and idle.

Tomorrow I get to find out how a cold start does. My gut tells me (I hope) that the IAC in the Zilla has been going bad, and that the replacement a month or so ago hadn't had time to 'learn' before I gave up and swapped back, writing it off to a bastardized setup.

I'll let you know tomorrow if there'* a lesson to be learned here.
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Old 12-17-2007, 04:34 AM   #2
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This learning that you mention - do you have the car learn with the IAC in P and D with AC off and then on, or what is your method?
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Old 12-17-2007, 09:51 AM   #3
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No, it takes several on/off ignition cycles and start cycles.

The FSM calls for a Tech 1 for the procedure.
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Old 12-17-2007, 09:57 AM   #4
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That is really interesting. I couldn't find anything about IAC learning on Alldata for the Boneville, but it showed 15 minutes of each P & D with AC on & off, and that'* it. Fords... So, I take it that a scantool would let you know if everything is spinning all right?
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Old 12-17-2007, 10:00 AM   #5
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A scantool will tell you if the IAC is moving (or being commanded to), and what 'counts' there are. It'* a stepper motor. It won't tell you if it'* 'right'. Your idle and AFR will tell you that.

If I didn't have a wideband O2, I wouldn't have known what the actual cause of the problem was in this case.

I guess I should go out and try a cold start. Coffee is ready.


brrrrrrr......
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Old 12-17-2007, 10:47 AM   #6
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Car started ALOT easier this morning. 3rd crank instead of the 6-10th. Making clear progress here. I'll drive it today and see if it'* any better tomorrow morning. I'll read up more on the IAC/PCM relationships in the meantime.
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Old 12-17-2007, 01:33 PM   #7
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Once you drive it and get the car up to temp and in TCC lock above 40 Mph the PCM should do an IAC learn.... From there it should idle good, and maybe start ok...lol

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